The objective of the present study was to evaluate the performance of guinea pigs in the growing period which were fed with diets formulated based on digestible energy (DE) or metabolized energy (ME), and with diets with different levels of metabolized energy and total protein. In the experiment 1, 50 male guinea pigs of 14 days of age were used and allotted randomly in two groups of 25 animals each group. Each group received during 21 days one of these diets: 1) diet with 2900 kcal of digestible Energy (DE) per kg and 2) diet with 2900 kcal of Metabolized Energy (ME) per kg. The results showed that animals which received diet 2 had better daily gain weight and feed efficiency (P<0.05) compared with those which received diet 1; nevertheless, feed intake was not affected (P>0.05) by the type of diet. In experiment 2, 90 guinea pigs of 14 days old where used and allotted randomly in 9 groups each one with 10 animals. Three levels of metabolized energy (2800.2900 and 3000 kcal/kg) were evaluated during 56 days; and also three levels of total protein (18, 19 and 20%) under a completely random design with a 3x3 factorial arrangement. At the end of the experimental period, 36 animals (4 per treatment) were slaughtered in order to determine the content of total protein and ether extract of the carcass. Results showed a significant (P<0.05) interaction between the metabolize energy levels and total protein, with the level of 2800 kcal ME/kg showing the poorest response. On the other hand, the dairy weight gain and the feed intake were influenced (P<0.05) by the ME level of the diet and not by the level of protein used (P>0.05). Feed conversion was not affected (P>0.05) neither by the levels of energy nor by the levels of protein. The content of total protein of the carcass was influenced (P<0.005) only by the level of ME of the diet, while the content of ether extract was not influenced by any dietary treatment. In conclusion, diets for guinea pigs in the growing period have to be formulated based on metabolized energy and not on digestible energy. Moreover, the diet with 3000 kcal ME/kg and 19 % of total protein showed the best performance in terms of daily gain weight